Jobs was apparently so paranoid about leaks that access to the
room was restricted even to Apple cleaning staff — only those
working on the "purple" project were allowed in.

From Wakabayashi's description, Jobs' infamous secrecy even
extended into the original iPhone team's lives outside the
company:

Mr. Jobs ordered employees working on the project at home to use
a computer in a secluded part of the house to prevent anyone from
accidentally seeing details. He also demanded that employees
encrypt digital images of the device.

Amazingly, much of the work the team did on the original iPhone
software wasn't even tested on actual iPhone hardware for most of
its development. Instead, they ran their early code on an
outdated Power Mac with hardware close enough to what the team
thought would be in the new phone. But because they also had to see what it
would feel like on a screen made for a phone, they had the
workstation hooked up to a tiny white 3.5-inch screen reminiscent
of the white iPhone the company announced 4 years later.